Measuring the radio frequency power associated with a wireless device is frequently necessary for production, final testing, repair, and other related activities. Typically, diode power meters and calorimetric power meters have been utilized to perform radio frequency power measurements associated with various cellular devices. Specifically, diode power meters are relatively well-suited to measure radio frequency power associated with continuous wave (CW) signals and other relatively narrow bandwidth signals (such as those signals associated with the AMPS standard). Calorimetric power meters are more suitable for broadband signals such as signals associated with code division multiple access (CDMA) signals.
An example of a diode power meter is shown in U.S. Pat. No. 5,656,929. The disclosed diode power meter switches a radio frequency (RF) detector between an input RF signal and a comparison RF signal to generate a difference signal. The difference signal is filtered, and converted into a direct current (DC) error signal by a synchronous detector that operates in step with the RF detector. The DC error signal is applied to an integrator to generate a loop control signal. The square of the loop control signal is linearly proportional to the input RF signal power when the servo loop is nulled, causing the comparison RF signal to equal the input RF signal.
A calorimetric power meter is a device that determines RF power utilizing, in general, a temperature-generated differential created by the signal being measured. An example of a calorimetric power meter is disclosed in U.S. Pat. No. 5,663,638. The disclosed calorimetric power meter accepts RF power into a terminating load that thermally couples generated heat to a temperature dependent resistance in one arm of a bridge. The imbalance created in the bridge produces an error signal within a servo loop. The servo loop responds by applying a direct current (DC) or low frequency power to a separate terminating load that couples heat into another arm of the bridge. The applied power is measured by metering how much power is required of the servo loop to re-balance the bridge. Calorimetric power meters are advantageous, because they measure total aggregate power contained in the signal. Thus, calorimetric power meters are suitable for wideband signals. However, calorimetric power meters suffer from certain limitations. Calorimetric power meters typically experience a relatively slow response time. Specifically, heat storage in the bridge limits the response time for the first power measurement, and after this measurement the bridge must be re-balanced by zeroing out the heat generated before a second measurement can be made. Accordingly, calorimetric power meters typically are unsuitable for wideband, non-repetitively pulsed signals such as occur in wide CDMA formats used for data applications.